What is the most effective avenue to voice my concerns?
When the FCC ran demos of broadband over power, it caused a tremendous amount of radio disturbance. Ham radio operators saw the disturbance on their licensed parts of the spectrum. They feared the FCC was killing Ham radio. So they wrote letters. Lots of letters. The FCC heard them and abandoned the trial of that technology.
Would these letters be of any use?
It usually goes something like this:
1) Comcast lobbyist: Hey politican, we'll donate 10k to your campaign this year, and another 100k+ if it becomes a tight race, just promise you'll vote against net neutrality if that ever happens, ok?
1a) Comcast, that's a deal.
2) Office Aid: Hey politican, after the FCC announced today, our phones are ringing off the hooks. People are really upset about this Net Neutrality thing.
2a) Okay, poll our constituents, and figure out just how many votes I'll lose if I vote for this thing.
3) If the number of votes > than the amount of votes the politican thinks (s)he can buy via the lobbyist's money, they change their position.
So your letters greatly affect step 2. Of course, its less cut and dry than above. Democratic politicans by and large believe in NN. Republican politicans these days rarely do. And polls are expensive and slow, so sometimes step 2a is skipped entirely and the politican makes a gut call based on the amount of feedback they receive.
But the point it, yes, your letters matter.